1. Field of the Invention
The present invention relates to a wire bonding apparatus and more particularly relates to a tension mechanism that applies tension to the wire.
2. Prior Art
A typical wire bonding apparatus is shown in FIG. 6.
A bonding head 2 is installed on an XY table 1 which is driven in X and Y directions on a horizontal plane. A raising-and-lowering mechanism 3 that is driven by a Z-axis motor (not shown) is installed on the bonding head 2 so that the raising-and-lowering mechanism 3 is moved up and down. A bonding arm 5, which holds a capillary 4 at its one end, and a damper supporting body 6 are fastened to the raising-and-lowering mechanism 3, and a damper 7 is disposed on the damper supporting body 6 so that the damper 7 is free to open and close.
Furthermore, a spool supporting body (not shown) that holds a wire spool 11 around which a wire 10 is wound, and a tension mechanism 20 which applies air tension to the wire 10, are provided on the bonding head 2. The wire 10 passes through the tension mechanism 20 and damper 7 from the wire spool 11 and further passes through the capillary 4. In FIG. 6, the reference numeral 15 refers to guide rails that guide lead frames 16.
The above type of bonding apparatus is disclosed in, for example, Japanese Patent No. 2617541 (Japanese Patent Application Laid-Open No. H2-122639).
The above-described bonding apparatus includes a tension mechanism that is shown in FIG. 5 with reference numeral 20C.
A tubular nozzle holder 62 is fastened by press-bonding to a main body 61. Inside the nozzle holder 62, a first nozzle 63 which has a through-hole 63a with a diameter that is slightly larger than the diameter of the wire 10 is disposed on the wire discharge side, i.e., on the capillary 4 side; and also a second nozzle 64 which has a through-hole 64a with a diameter that is larger than the diameter of the through-hole 63a is disposed on the wire supply side, i.e., on the wire spool 11 side. An air passage 64b is formed in the undersurface of the second nozzle 64, and a conical air exhaust passage 64c is formed in the upper surface of the through-hole 64a. 
The first nozzle 63 is held by a first nut 70 that is screw-engaged with the nozzle holder 62. The second nozzle 64 is pressed downward by a second nut 71 which is screw-engaged with the nozzle holder 62, so that this second nozzle 64 is in pressing contact with the first nozzle 63. A wire guide 72 is fastened to the first nut 70 by press-bonding. A guide hole 72a is formed in the wire guide 72. The inner diameter of the guide hole 72a is larger than that of the through-hole 63a. Furthermore, a conical wire passage opening 72b is formed in the undersurface of the wire guide 72.
A recess-form air passage 64d is formed in the outer circumference of the lower part of the second nozzle 64. The air passage 64d communicates with the air passage 64b. A recess-form air passage 62a that corresponds to the air passage 64d is formed in the outer circumference of the nozzle holder 62. Furthermore, an air passage 62b is formed so as to communicate with the air passage 64d. An air supply passage 61a is formed in the main body 61 so as to communicate with the air passage 62a. A pipe coupling 73 is screwed into the air supply opening of the air supply passage 61a. A hose (not shown) is connected to the pipe coupling 73, and this hose is connected to an air supply source via an electromagnetic valve and a mechanical valve.
The action of the tension mechanism 20C will be described below.
When compressed air is supplied from the pipe coupling 73, the compressed air flows into the air passage 64b via the air supply passage 61a and air passages 62a, 62b and 64d. Since the diameter of the through-hole 64a of the second nozzle 64 is larger than the diameter of the through-hole 63a of the first nozzle 63, the compressed air that flows into the air passage 64b flows through the through-hole 64a and is discharged from the air exhaust opening 64c. As a result of the fluid resistance of the flow from the bottom to top through this through-hole 64a, a constant tension is applied to the wire 10 in the direction of the second nozzle 64 from the first nozzle 63.
The tension mechanism 20C is generally used in loop formation step during wire bonding. In other words, a loop is formed by first bonding a ball at the tip end of the wire 10 to a first bonding point and then by raising, moving and lowering the capillary 4 so that the capillary 4 is positioned at a second bonding point; and during these steps, tension is applied to the wire 10 by the tension mechanism 20 so that the wire 10 is not paid out from the lower end of the capillary 4 to an excessive extent.
Examples of wire bonding apparatuses equipped with a tension mechanism 20 as described above are disclosed in Japanese Patent No. 2617541 and Japanese Patent Application Laid-Open (Kokai) Nos. S58-218131 and H7-221133.
As disclosed in the above prior art, the tension adjustment is accomplished by valve adjustment in order to adjust the flow rate of the compressed air that is supplied to the pipe coupling 73. However, this adjustment is a fixed adjustment that is fixed beforehand for a particular work on which the bonding is performed, prior to the start-up of the wire bonding apparatus. Thus, it cannot meet the changes in the wire diameter, loop shape and wire length (i.e., the length of the wire corresponding to the distance between the first bonding point and second bonding point) that occur during wire bonding. As a result, the optimal loop shape for each wire that is connected is not obtained.
Accordingly, the object of the present invention is to provide a wire bonding apparatus that controls the tension applied to the wire in a plurality of different stages or strength during wire bonding, thus forming a better loop shape.
The above object is accomplished by a unique structure for a wire bonding apparatus that comprises a wire spool around which a wire is wound, a capillary through which the wire is passed, and a tension mechanism which is disposed between the wire spool and the capillary so as to apply a back tension to the wire; and the unique structure is that:
the tension mechanism is comprised of:
a first nozzle which has a through-hole through which the wire passes and second and third nozzles which respectively are provided with through-holes that have a diameter greater than the diameter of the through-hole of the first nozzle, the second and third nozzles being disposed above and below the first nozzle,
a first air passage formed in the joining surfaces of the first nozzle and the second nozzle, and
a second air passage formed in the joining surfaces of the second nozzle and the third nozzle;
a compressed air supply means is provided so as to supply compressed air to the first air passage from an air supply source; and
a vacuum suction means is provided so as to supply vacuum suction to the second air passage from a vacuum supply source.
The above object is further accomplished by another unique structure for a wire bonding apparatus which is equipped with a wire spool around which a wire is wound, a capillary through which the wire is passed, and a tension mechanism which is disposed between the wire spool and the capillary and which applies a back tension to the wire; and the unique structure is that
the tension mechanism is comprised of
first and third nozzles which have through-holes through which a wire passes and second and fourth nozzles which respectively have through-holes that have a diameter greater than the diameter of the through-holes of the first and third nozzles and through which the wire passes, the third nozzle, fourth nozzle, first nozzle and second nozzle being disposed in this order from the bottom to the top,
first and second air passages respectively formed in joining surfaces of the first nozzle and the second nozzle and in joining surfaces of the third nozzle and the fourth nozzle, and
an air exhaust passage which communicates with an outside and is formed in joining surfaces of the fourth nozzle and the first nozzle; and
a compressed air supply means is provided so as to supply compressed air to the first and second air passages from an air supply source.